Long-Term Stability at −20°C of Aspergillus Galactomannan in Serum and Bronchoalveolar Lavage Specimens

Abstract

Research to develop and validate novel methods for diagnosis of aspergillosis based on detection of galactomannan requires the use of clinical specimens that have been stored frozen. Data indicating that galactomannan remains stable when frozen are scant. The objective of this study was to determine the stability of galactomannan in clinical specimens stored at -20 °C that were positive in the Platelia Aspergillus enzyme immunoassay when initially tested. Prospective real-time testing of serum and bronchoalveolar lavage (BAL) fluid pools from positive and negative patient specimens showed no decline in galactomannan index (GMI) over 11 months at -20 °C and no development of positive reactions in the negative-control pool. Retrospective testing of positive specimens that had been stored at -20 °C for 5 years showed that 28 of 30 serum (n = 15) or BAL (n = 15) specimens remained positive. These findings support the use of frozen serum or BAL specimens stored for at least 5 years in evaluation of diagnostic tests based on detection of galactomannan.